4.8 v or 6 v receiver packs ?

[Martin McIntosh]

I know the OP is using 148`s at the moment but the question was `why is everyone else using 6V?`. One lost cell from four = failsafe = crash. One from five would have no immediate effect. So called analogue servos seem to be being phased out anyway.

Another good reason is that if a servo got overloaded for any reason it would drop the voltage.

I got caught out twice on the same analogue equipped model due to a cell failure in each case and have never used 4.8V since.

[Cuban8]

Posted by Martin McIntosh on 17/11/2017 10:24:18:

I know the OP is using 148`s at the moment but the question was `why is everyone else using 6V?`. One lost cell from four = failsafe = crash. One from five would have no immediate effect. So called analogue servos seem to be being phased out anyway.

Another good reason is that if a servo got overloaded for any reason it would drop the voltage.

I got caught out twice on the same analogue equipped model due to a cell failure in each case and have never used 4.8V since.

Never used 4 cell packs for ages now since I discovered a couple of my packs had single bad cells that were effectively reducing the packs performance by well over a half. As said above, if you have a weak cell in a 6V pack you'll almost certainly be OK. In either case, check the performance of RX batteries regularly, it's not difficult and can be performed with a simple four-button charger. As for digital servos, so far I've never found the need to use them - for a servo with a bit of extra grunt the Futaba 3010 (6Kg) is quite sufficient and not at all expensive.

Do beware of 2S LiFes though, a couple of my high torque Hitecs went barmy at anything over 6.5V - Futabas seem OK.

Edited By Cuban8 on 17/11/2017 11:39:28

[Don Fry]

Thank you for my continued education.

[Paul Marsh]

I'm using more Dual battery systems now, for what it costs, having not one 6v, but two 6v batteries powering your gear through a Dual regulator switch and even using two elevator servos -

[extra slim]

I do similar to Paul, but I see on larger models quite a few use two different switches as well, and mine and Pauls setup does I guess give the switch as the single point of failure.. Its how far you go.. larger models can cope with the extra weight.

[Former Member]

[This posting has been removed]

[Martin Harris - Moderator]

I've just tried a quick test and (on my 2.4GHz radio system) the test servos (one digital, one analogue) stopped responding (at 4.11v and 3.79v supply respectively - measured in the receiver at 3.85v and 3.67v*) well before the receiver lost its link with the transmitter as I reduced the supply voltage to below 3.37v. Once the link was lost, increasing the supply voltage instantly restored the telemetry link (there's no easy way to tell if the uplink had been lost and failsafe had initiated as the servos had long since gone to sleep).

In practice, a failing cell in a pack should make itself known by erratic servo response (and in the case of telemetry equipped models, alarms) before loss of communication with the receiver.

I find it a little intriguing that losing one cell in a 4 cell pack means potential disaster while using a 2S LiFe is acceptable - I don't know what the typical failure mode of a LiFe cell is (if there is one!) but a pack dropping to 3.3v doesn't sound encouraging! That is the reason why my preferred power solution for larger/more valuable models is paralleled LiFe packs and switches.

Percy's is a good point but I suppose the answer is that the transmitter battery lives in a much kinder environment and is almost universally monitored for voltage level.

* The measured voltages at the supply and from the receiver telemetry were within 0.02v of each other with no servo loads at both the high and low points which illustrates the voltage drops in the wiring and receiver with the servos in operation.

Edited By Martin Harris on 17/11/2017 19:32:14

[Martin McIntosh]

MH, that is exactly why I now use two 2S Life packs via a Failover switch on most of the more valuable models. Better than a twin NiMh/twin mechanical switch set up which gives some redundancy but is not foolproof unless diodes are fitted to each pack which would reduce the voltage from them by 0.7V which at 6V is acceptable.

The disadvantage is the size of the Failover switch. I use 2S 700mA/hr packs unless I need weight at the nose when I go way over the top and use 2x 1800 LiFe packs. These are so incredibly cheap at the moment that you can afford to replace them annually. Where possible I also use LiFe pack on my Tx`s where they seem to last almost forever. Another disadvantage though is that a battery checker will always show them as fully charged until they fall off the cliff.

[Geoff S]

I think the most likely failure is the mechanical switch rather than the chemical battery pack, always provided it was up to the job in the first place. That particularly applies to liquid fuelled models, with single cylinder petrol being the worst as regards vibration. On my Maher's Thunderbird, which has a Zenoah 26 petrol engine with magneto ignition I have a single sub C 4.8v battery pack but 2 toggle switches in parallel which are each checked before each flight. All the servos are hefty analogue.

On my electric models I don't have a switch and rely totally on the flight pack connection. Obviously, just one battery, although my Ezee Pezee needs 2 batteries in parallel to get the CoG right

Geoff